Proteoglycans (PGs) and collagen are important macromolecules of the skin, as of most connective tissues. Interactions between them may contribute to the structural organization of the intercellular matrix of the skin. So far only a few studies on skin PGs have appeared, and in these the PGs were extracted under conditions which might cause structural changes in complex molecules. They suggested, however, the presence of two glycosaminoglycans, namely chondroitin sulfate and dermatan sulfate, as major components of the PGs. Although work on cartilage PGs has provided a model for structure and interaction, it should be recognized that PGs from other tissues may be quite different in chemical nature and organization. In skin the marked interaction of PGs with collagen may imply a relationship with functional importance in normal and pathological conditions. We have isolated and purified PGs from pig skin under mild conditions, and we find distinct types, one containging chondrotitin sulfate and the other dermatan sulfate. The former has been examined for aggregation in the presence of hyakyribuc acid (as is observed with cartilage PG), and no indication of interaction was found. Some of the chemical and physical properties of this PG have been determihed, and we plan to continue a detailed study of the heterogeneity of the two or more PGs, the nature and spatial arrangement of the glycosaminoglycan chains on the protein core, and the possible self-aggregation of the PGs and their interactions with collagen or tropocollagen. we expect, also, to compare immunological properties of these PGs with each other and with PGs from other tissues or species. Our long-range goal is to learn more about the ultrastructure of the skin under normal and pathological conditions and possibly during aging.